Output driver impedance calibration circuit
AssigneeInternational Business Machines Corporation
InventorWilliam F. Lawson
Life of this patent
Estimating the term…
Abstract
An output driver impedance calibration circuit which is used to make I/O (input/output) off chip driver characteristics, for a plurality of output driver circuits, alike on the same chip. The output impedance of an input/output driver circuit is calibrated by providing an external target impedance reference (it could be a multiple of the actual target output impedance), multiple devices in the output stage of the I/O driver circuit, a circuit to determine the value of the actual output impedance as compared with its target output impedance and a determination of when to stop the calibration process.
Claims14
An output driver impedance calibration circuit comprising:
- an output driver circuit having an output stage with a base transistor device;
- a plurality of calibration transistor devices in the output stage of the output driver circuit;
- means for activating in a time ordered sequence the base transistor device and then one at a time in the time ordered sequence each of the plurality of calibration transistor devices;
- means for providing a target reference voltage;
- a voltage comparator circuit for comparing the value of an output voltage of the output stage of the output driver circuit with the target reference voltage;
- means for storing the states of the plurality of calibration transistor devices when the output voltage attains the target reference voltage, to preserve the states of the plurality of calibration transistor devices and to calibrate the output impedance of the output driver circuit to a target output impedance.
Dependencies are inferred from the claim text.